Method of plating a wafer

ABSTRACT

A plating method for forming a uniform magnetic film in conducting a plating treatment on a wafer with a magnetic film of, for instance, a Fe—Co-based alloy. Specifically, the method comprises the steps of supplying a plating solution through a plating-solution-supply section of a plating tank to a wafer, which placed on an opening of the plating tank, and conducting a plating treatment on the wafer while the plating solution is kept in contact with a plating target surface of the wafer, wherein the plating solution employed is one forming a magnetic film, and the plating treatment is done while a magnetic field is applied to the plating solution in contact with the plating target surface of the wafer.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a treatment technology of plating a wafer, and especially to a method of plating a wafer in forming a magnetic film, such as for example a Fe—Ni-based alloy and Fe—Co-based alloy.

2. Description of the Related Art

As an apparatus for plating a semiconductor wafer, a cup-shaped plating apparatus has been known conventionally. The cup-shaped plating apparatus supplies a plating solution through a plating-solution-supply section of a plating tank to a wafer, which is placed on an opening of the plating tank, thereby conducting a plating treatment on the wafer while the plating solution being kept in contact with a plating target surface of the wafer.

The plating apparatus, in which a plating solution is supplied with an upward flow toward a plating target surface of a wafer, allows the plating solution to be in contact with the plating target surface in a manner the solution spreads flowingly in a peripheral direction from a central area of the target surface, so that uniform plating can be advantageously done to a whole plating target surface. This kind of plating apparatus has been widely used as suitable for small lot production and automated plating treatment because it allows wafers being placed onto a wafer supporting section to be changed in series for the purpose of plating treatment, as for example disclosed in Patent Document 1, i.e. Japanese Patent Application Laid-open No. 350185/1999.

In recent years, semiconductor wafers have been processed to provide various kinds of electronic parts, and thus various types of plating treatments are conducted in tune with many purposes. As a processing technology of a wafer, formation of a magnetic film on a surface of a wafer is in operation. In forming the magnetic film, for example a plating treatment using a Fe—Ni-based alloy known as permalloy or a Fe—Co-based alloy is sometimes performed on a wafer.

In such a plating treatment where the magnetic film should be formed onto a wafer, more uniform plating film is demanded. Specifically, with the recent development of a processing technology of a fine wiring, an extremely highly accurate plating treatment is demanded to a magnetic film, which is to be applied to a surface of a wafer, and thus a technology enabling more uniform plating film to be formed on a plating target surface of a wafer is demanded. Furthermore, the wafers themselves have been becoming bigger in diameter recently, thereby a plating technology, which forms a uniform magnetic film is desired even if an area of a wafer to be plated is so large.

SUMMARY OF THE INVENTION

The present invention was made against the above-discussed technical background, and it is an object of the invention in the conventional treatment technology of plating a wafer to provide a plating method, which enables a uniform magnetic film to be formed in conducting a plating treatment on a wafer with a magnetic film such as a Fe—Ni-based alloy, a Fe—Co-based alloy or the like.

In order to solve the above problem, the present invention defines a plating method for conducting a plating treatment on a wafer, comprising the steps of supplying a plating solution to a wafer, which is placed on an opening of a plating tank, through a plating-solution-supply section of the plating tank, and conducting a plating treatment on a wafer while making the plating solution in contact with a plating target surface of the wafer, characterized by employing a plating solution for forming a magnetic film, and conducting a plating treatment while applying a magnetic field to the plating solution in contact with the plating target surface.

As a method of applying a magnetic field in the present invention, it is preferable to do by arranging a magnetic body on an opposite surface of the plating target surface of a wafer. More specifically, a magnetic field can be applied in the present invention by arranging permanent magnets or electric magnets on an opposite surface of the plating target surface of a wafer. Arrangement of such magnetic bodies allows a Lorentz force to be wielded to plating ions in the plating solution, thereby achieving an electrodeposited condition not subject to flow of a plating solution and formation of a uniform magnetic film on the plating target surface of a wafer.

In the present invention, it is preferable that the magnet film is formed with a Fe—Ni-based alloy or a Fe—Co-based alloy. If it is a Fe—Ni-based alloy, a Fe—Ni-based alloy plating solution containing nickel sulphate, nickel chloride, ferrous sulphate, and boric acid can be employed. When such a Fe—Ni based alloy plating solution is employed, it is preferable if the conditions of a plating treatment are 2-10 A/dm² in terms of current density, 50-65° C. in terms of liquid temperature, and 3.0-3.8 in terms of pH. Alternatively, if it is a Fe—Co-based alloy, the preferable is a Fe—Co-based alloy plating solution containing iron perchlorate (II) hexahydrate, perchlorate cobalt (II) hexahydrate, ammonium chloride, sodium hypophosphite hydrate, and ascorbic acid. When such a Fe—Co-based alloy plating solution is employed, it is preferable if the conditions of a plating treatment are 2-10 A/dm² in terms of current density, 50-65° C. in terms of liquid temperature, and 3.0-3.8 in terms of pH.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of the cup-shaped plating apparatus according to First Embodiment of the present invention;

FIG. 2 is a plane configuration view of a permanent magnet of a wafer depressing machine according to First Embodiment of the present invention; and

FIG. 3 is a cross-sectional view of a wafer depressing machine of the cup-shaped plating apparatus according to Second Embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, preferred embodiments of the plating method according to the present invention will be concretely described with reference to the drawings.

First Embodiment

FIG. 1 is a cross-sectional view, which shows schematically a plating tank of the cup-shaped plating apparatus according to First Embodiment. As shown in FIG. 1, the cup-shaped plating apparatus according to the present embodiment has a wafer-supporting section 2 provided along an upper opening of a plating tank 1, onto which the wafer-supporting section 2 a wafer 3 is to be placed, and a plating treatment is carried out on a plating target surface 4 of the wafer 3. Disposed on the wafer-supporting section 2 are a ring-shaped cathode electrode 5 and a ring-shaped seal packing 6, both being adapted to make contact with a periphery of the wafer 3.

At the center of a bottom of the plating tank 1, a solution-supply pipe 7 is provided. Below the wafer-supporting section 2, a solution-discharge pipe 8 for discharging a plating solution outside the plating tank 1 is provided. Therefore, a plating solution supplied in upward flow through the solution-supply pipe 7 reaches near the center of the plating target surface 4, and will form a flow as indicated by arrows shown in FIG. 1, which spreads in a direction toward periphery of the wafer 3. Around the solution-supply pipe 7, there is provided an anode electrode 9 in a manner opposed to the plating target surface 4 of the wafer 3.

Further, above the plating tank 1, there is provided a vertically moveable wafer-depressing machine 11 having permanent magnets 10, which arrange an N pole and S pole in a horizontal direction of a wafer on an upside surface, namely an opposite side of the plating target surface 4 of the wafer. As FIG. 2 shows, permanent magnets 10 have a plurality of rod-like permanent magnets 101 disposed so as to form a magnetic field on the entire area of the plating target surface 4 of the wafer 3. In the case of First Embodiment, it is formed a magnetic field, which provides magnetic field lines advancing from the N pole to S pole in a horizontal direction with respect to the plating target surface 4 of the wafer 3, as indicated by a two-dot broken line in FIG. 1. A thin protective material 12 made of silicon rubber is provided on a downside of the permanent magnets 10 equipped on the wafer-depressing machine 11 in order to prevent the permanent magnets 10 from being damaged by a direct contact with the wafer 3.

Second Embodiment

Second Embodiment relates to an embodiment where a circular permanent magnet 10′ having an essentially identical shape to the plating target surface of a wafer is disposed in place of the rod-like permanent magnet in First Embodiment. In this Second Embodiment, all but the permanent magnet 10′ arranged on the wafer-depressing machine 11 are the same as First Embodiment, so that specific showing in the figure and description are omitted. In this Second Embodiment, a magnetic field which provides lines of magnetic force advancing from N-pole to S-pole in a vertical direction in terms of the plating target surface 4 of a wafer 3. See two-doted dash lines in FIG. 3.

It should be noted that permanent magnets are employed as an example in the above First and Second embodiments, however electric magnets of soft iron for instance can also be employed.

Lastly, description is made with respect to a result of a plating treatment on a wafer with use of the cup-shaped plating apparatuses of the above First and Second embodiments. The wafer employed in a plating test has a seed metal of Cu provided on the plating target surface thereof, and has a diameter of 200 mm.

As a plating solution, a Fe—Ni-based alloy plating solution having the following compositions.

Nickel sulfate 100 g/L Nickel chloride 50 g/L Ferrous sulfate 12 g/L Boric acid 50 g/L pH 3.2 Liquid temperature 60° C. Current density 5 A/dm² Amount of liquid supplied 4 L/min.

A plating treatment was performed so that a plating thickness becomes 10 μm.

In First Embodiment, a total of five rod-like permanent magnets having a size of 10 mm×10 mm in cross section were arranged in a manner illustrated in FIG. 2 and were used. A magnetic flux density of the permanent magnets employed was 40 gauss. In Second Embodiment, a discoid permanent magnet having a diameter of 120 mm and thickness of 10 mm was arranged in a manner so that the N pole should face a wafer as illustrated in FIG. 3 and was used. A magnetic flux density of the permanent magnet employed was also 40 gauss.

As a result, in the cup-shaped plating apparatuses of First and Second Embodiments, it was found that an entire plating target surface of the wafer had been formed with a magnetic film consisting of a Fe—Ni alloy, which has uniform thickness and good appearance. 

1. A method of plating a wafer comprising the steps of supplying a plating solution through a plating-solution-supply section of a plating tank to a wafer, which wafer is placed on an opening of the plating tank, and conducting a plating treating on the wafer while the plating solution is kept in contact with a plating target surface of the wafer, wherein said plating solution employed is one forming a magnetic film, and said plating treatment is done while a magnetic field is applied to the plating solution in contact with the plating target surface of the wafer.
 2. The method of plating a wafer according to claim 1, wherein the step of applying a magnetic field is conducted by arranging at least one magnetic body on an opposite surface of the plating target surface of the wafer.
 3. The method of plating a wafer according to claim 1, wherein said magnetic film is either a Fe—Ni-based alloy or a Fe—Co-based alloy.
 4. The method of plating a wafer according to claim 2, wherein said magnetic film is either a Fe—Ni-based alloy or a Fe—Co-based alloy. 